Isolation and Partial Characterization of Three Classes of Mutant in Pseudomonas syringae Pathovar pisi with Altered Behaviour towards Their Host, Pisum sativum

SUMMARY: Mating with Escherichia coli strain SM10 carrying the Tn5 vector pSUP2011 was used to mutagenize Pseudomonas syringae pv. pisi strain 299A. The resulting transconjugants were each tested by stem-inoculation into several pea (Pisum sativum) cultivars. Three classes of mutant, which probably resulted from insertion of part or all of RP4-2-Tc:: Mu into the genome of strain 299A, showed reduced virulence towards one or more pea cultivars. The single class I mutant was avirulent on all pea cultivars tested and had lost the ability to induce a hypersensitive response in tobacco (Nicotiana tabacum) cv. White Burley; the single class II mutant induced a hypersensitive response on all pea cultivars and tobacco; class III mutants showed reduced virulence towards pea cv. Early Onward, while remaining fully virulent towards other normally susceptible pea cultivars, and inducing a hypersensitive response in tobacco.